Semiconductor memories and magnetic memories are mainly used for storage (recording) devices of information apparatuses. The semiconductor memories are used for internal storage devices from the viewpoint of access time, while magnetic disk drives are used for external magnetic storage devices from the viewpoint of their large storage capacity and non-volatility. The storage capacity is an index indicating performance of the magnetic disk drive. In line with the recent development in the information society, there is an emerging market need for compact magnetic disk drives offering large storage capacities. Perpendicular recording is suitable for this market need. For its ability to achieve high-density recording, the perpendicular recording system is considered to become the mainstream, supplanting conventional longitudinal recording.
Japanese Patent Publication No. 2006-120223 (“Patent Document 1”) and Japanese Patent Publication No. 2005-310363 (“Patent Document 2”) disclose magnetic heads for perpendicular recording, in which the shortest distance between a main magnetic pole piece and soft magnetic films disposed on both sides thereof is longer than the shortest distance between the main magnetic pole piece and a soft magnetic film disposed on a trailing side thereof. Japanese Patent Publication No. 2004-326990 (“Patent Document 3”) discloses a magnetic head for perpendicular recording, in which the shortest distance between a main magnetic pole piece and an auxiliary magnetic pole piece is one to five times as long as the distance in surface between a soft magnetic film disposed on a lower surface of a recording medium and the main magnetic pole piece.
In magnetic recording media of the perpendicular recording system, magnetization occurs in a direction perpendicular to the surface of the medium. As a result, effect from demagnetizing field acting between adjacent magnetic domains is relatively smaller than the longitudinal recording system. This allows high-density magnetic information to be recorded on the medium, achieving a magnetic disk having a large storage capacity.
To make the most out of this characteristic of the perpendicular magnetic recording medium, there is a shield disposed on the trailing side of the main magnetic pole piece, so that a recording magnetic field has a precipitous magnetic field gradient. In addition, to prevent the recording magnetic field from leaking to adjacent tracks, shields are provided on both sides of the main magnetic pole piece.
A shield structure is embodied in the art disclosed in Patent Document 1 as the magnetic head for perpendicular recording, in which the distance between the main magnetic pole piece and the shield on the trailing side is shorter than the distance between the main magnetic pole piece and the side shield. Similarly, a shield structure is embodied in the art disclosed in Patent Document 2 as the magnetic head for perpendicular recording, in which the distance between the main magnetic pole piece and the shield on the trailing side is shorter than the distance between the main magnetic pole piece and each of the side shields disposed on both sides of the main magnetic pole piece. Meanwhile, Patent Document 3 discloses the magnetic disk drive, in which the distance between the main magnetic pole piece and the auxiliary magnetic pole piece for returning a magnetic flux from the medium is one to five times as long as the shortest distance between the soft magnetic underlayer surface of the magnetic disk and the main magnetic pole piece.
The above-referenced conventional art techniques are considered effective in promoting even higher densities in perpendicular magnetic recording. The conventional art techniques, however, do not mention techniques to optimize the distance between the main magnetic pole piece and side shields, and between the main magnetic pole piece and the trailing shield. There is therefore a problem in that recording densities are not as much improved as expected depending on conditions of the soft magnetic underlayer and perpendicular recording layer that constitute the perpendicular magnetic recording medium.